1. Field of the Invention
The invention relates to data processing systems and more particularly to apparatus for indicating the device having the highest priority for a given set of device requests.
2. Description of the Prior Art
Computing systems, in general, include a processor and a plurality of input/output devices. Since a number of devices may request operation with the processor at the same time a system of priorities must be established so that the processor can operate with the I/O devices in an orderly fashion.
Prior art systems have solved the priority problem in a myriad of ways including elaborate hardware techniques, hardware/firmware techniques, software techniques, etc.
Some typical U.S. Patents (although not necessarily the closest prior art) relating to priority resolving devices are as follows:
These systems have been designed for large computer systems and are costly in terms of hardware and in terms of time to select the input/output device. Also, the priority system implemented is not readily changeable. The problem is compounded when the input/output devices are communication lines, each having the capability of receiving and transmitting in different modes, synchronous, asynchronous and at different bit rates.